refactor: restructure nginx config into per-app files (#1)

## Summary

- Added `push.sh` script to deploy configs to prod via `sudo rsync` (with `--delete` for exact mirroring)
- Split the monolithic `conf.d/server.conf` (1,682 lines, 96 server blocks) into 28 per-app files under `sites-available/`, with corresponding symlinks in `sites-enabled/`
- Extracted custom `nginx.conf` settings (`log_format` directives, `server_names_hash_bucket_size`) into dedicated `conf.d/logging.conf` and `conf.d/tuning.conf` files, leaving `nginx.conf` as close to stock as possible

## Test plan

- [x] `sudo nginx -t` passes on prod after the sites-available restructure

✨ This PR was created with help from Hikari~ 🌸

Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Reviewed-on: #1
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

pull.sh

@@ -1,7 +1,3 @@
-servers=("prod" "gitea")
-
-for server in "${servers[@]}"
-do
-    echo "Pulling $server"
-    rsync --archive --verbose $server:/etc/nginx/conf.d/server.conf configs/$server.conf
-done
+echo "Pulling prod nginx"
+rsync --archive --verbose prod:/etc/nginx nginx
+echo "All done!"